Method and furnace for heat treating minerals



April 11, 1967 R. D. FRANS 3,313,534

METHOD AND FURNACE FOR HEAT TREATING MINERALS Filed July 21, 1965 0 0!) 0 0 o 0 oo 0 o JQMC P F United States Patent 3,313,534 ltiETHGD AND FURNACE FOR HEAT TREATING MHVERALS Robert D. Frans, Brookfield, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis. Filed July 21, 1965, Ser. No. 473,776 19 Claims. (Cl. 263-32) The present invention relates to a method and apparatus for heat treating minerals which may be used, for example, to burn limestone to lime, limestone and clay to Portland cement and water bound agglomerates of iron ore to produce hard abrasive resistant agglomerates. The invention provides improvements in the methods and apparatus disclosed in U.S. patent to W. F. Stowasser, lr., 2,925,336 and U.S. patent to E. Bade, 3,110,751.

The Stowasser and Bade patents disclose systems in which minerals are deposited upon a traveling grate and carried through a drying chamber, a preburning chamber and then are deposited in a rotary kiln for final burning. Hot gases in the kiln heat minerals to high temperatures and then pass from the kiln to preburn and then dry the material before passing up a stack at relatively low temperatures. Many materials have been successfully turned in such equipment and iron ore, limestone, and limestone with clay are merely a few examples.

One problem involved in the operation of such systems as disclosed in the Stowasser and Bade patents is that of obtaining proper thermodynamic balance of heat inputs between the drying, preburning and final heating stages. This problem arises because for each material there are these requirements that establish desired temperatures within such systems. The first requirement is that for each material there is a known or ascertainable Btu. input and temperature level to which the material must be finally heated in the rotary kiln. The second requirement is that each material also has a known or ascertainable temperature level and total heat input that is necessary to achieve the desired preburn before the material is exposed to much higher temperatures in the kiln. The third requirement is that each material also has a lmown or ascertainable desirable maximum gas temperature for drying the ore so that water vapor is not produced so rapidly that the material breaks into particle sizes so small that excessive dust is created. Thus a material requiring a relatively low drying temperature (to prevent particle break up) will require a relatively large volume of gases (to completely dry the material) and a material that can tolerate a relatively high drying temperature may require a relatively small volume of drying gases. Although some materials burn with partly exothermic reactions (for example magnetite iron ore), it is nevertheless true for all materials that the temperature of gases that perform the final heating is a determing factor as to the temperature of gases discharged from the kiln for preburning and drying material on the grate. Therefore the degree to which the first requirement is achieved affects the degree to which the second and third requirements can be achieved. A problem of proper thermodynamic balance between the drying, preburning and final heating stages is created because the gas flow begins with a specific volume of preheated gas from the cooler mixing with burning fuel in the kiln to meet the first requirement and it is rare or perhaps never happens (according to the practices of the prior art) that the volume and temperature of the gases finally reaching the drying chamber are what is wanted to meet the third requirement.

It is, therefore, an object of the present invention to provide a new and improved apparatus for drying, preburning and final heating of minerals, with means for ICC controlling and improving the thermodynamic balance between the drying, preburning and final heating stages.

Another problem involved in the operation of such systems as are disclosed in the Stowasser and Bade patents is the matter of ringing in the kiln. A ringlike deposit of dust size particles of the material tends to build up on the inner surface of the kiln. This deposit reduces kiln volume and results in the kiln drive carrying a nonproductive and useless load. In plants constructed and operated according to prior art teachings this problem periodically necessitates a plant shutdown to remove the deposit or attempts to remove such deposits while the plant is in operation. There are two ways that such deposits can be removed while a plant is in operation but neither are entirely satisfactory. One way is use a boring bar inserted through the material discharge end of the kiln (i.e., the burner end); Such boring bars however cannot reach far enough into the kiln to remove all of the deposit. A second way is for the operator to shoot into the kiln with a shotgun. The disadvantages of shooting are that chunks of the deposit are dislodged that are of irregular size and shape and the cost of shooting and disposing of the chunks currently amounts to (for iron ore) about eight cents per ton of material processed.

It is therefore another object of the present invention to provide a new and improved apparatus for drying, preburning and final heating of materials with means for controlling, to Within tolerable limits, the build-up of a deposit on the inner surface of the kiln. I

Still another problem involved in the operation of such systems as disclosed in Stowasser and Bade patents is the matter of controlling and eliminating unwanted mineral constituents which include: arsenic and arsenic oxides in iron ore; potassium and sodium oxides (alkali) in cement; and sulfur in lime. These are examples of materials that are volatilized during high temperature final heating in the kiln but tend to be redeposited on or chemically react with the material being preburned on the grate or gas borne dust particles which according to prior art practices are filtered out of the gas stream as it passes through material being preburned.

It is therefore still another object of the present invention to provide a new and improved apparatus for drying, preburning and final heating of materials with means for eliminating unwanted mineral constituents that are volatilized during final high temperature heating.

According to a preferred embodiment of the present invention an exhaust opening is provided in the furnace structure that defines the preburning chamber over the traveling grate. A portion of the hot gases coming from the kiln and passing into the preburn chamber are withdrawn through this opening to bypass the withdrawn portion of the hot gases away from the material in the preburn chamber while the remainder of the hot gas coming from the kiln is permitted to pass through the material in the preburn chamber. Withdrawing some of the gases from the preburn chamber unloads most of the dust from the system. In most operations the temperature of such withdrawn gases will be in a range from about 1600 to 2100 degrees Fahrenheit. This hot dust laden gas is then mixed with cold air (at atmospheric temperature) to drop the temperature to below about 850 degrees Fahr enheit. The other gas flow, passing through the material in the preburn zone, transfers heat to the material therein and this gas drops in temperature to an average temperature of about 750 degrees Fahrenheit. This gas that has passed through the material in the preburn chamber and the gas that has bypassed the preburn chamber are then mixed, then directed through one or more cyclone dust collectors and then delivered to the inlet of a fan which discharges the gas to one or more chambers in which the material is treated before passing into the preburn chamber. A damper controls the withdrawal of the bypass gas to provide the desired fiow through material in the preburn chamber. Another damper controls the cold air which is mixed with the gas that has bypassed the grate in the preburn chamber so the volume and temperature of the mixed gases made available for treating material before it enters the preburn chamber is that which is most desirable for the particular material being treated. For some materials (for example hematitic iron ore) the amount of gas bypassing the preburn chamber in order to provide the desired volume and temperature for treating material before it enters the preburn chamber, will leave insufiicient hot gas passing through the material to accomplish the desired preburn. In such operations one or more auxiliary burners may be mounted in the furnace structure defining the preburn chamber to make up the heat deficit.

The furnace system disclosed in the Stowasser and Bade patents has been successfully applied on commercial scale to process many materials, including iron ore, cement, and lime. Further, the furnace disclosed in the Bade patent is known to be capable of extracting arsenic from iron ore when operated as disclosed in the Bade patent. Comparative tests were therefore performed with such equipment and equipment constructed in accordance with the present invention. It was found that the present invention provided much better control of the thermodynamic balance, significantly reduced ringing in the kiln and produced a twentyfold increase in the amount of arsenic extracted from arsenic containing iron ore.

Other objects, advantages and the manner in which such are attained will be apparent from the following description with reference to the drawing which diagrammatically discloses a furnacing system according to the present invention.

Referring to the drawing, raw material is prepared for the furnace by a suitable agglomerating device which may be, as shown for example, a balling device B. A feeder F deposits the prepared raw material on a gas pervious traveling grate 1. A housing structure 2 is arranged to enclose a space over the grate 1. A bafiie Wall 3 is subtended from the roof of housing 2 to a predetermined distance above grate 1. Bafile wall 3 divides the space enclosed by housing 2 into a preconditioning chamber 4 and a preburn chamber 5. An auxiliary heat inlet 6 may be mounted to direct a flame (or heat from an auxiliary combustion chamber, not shown) into preburn chamber 5. Raw material on grate 1 will be transported through preconditioning chamber 4, then preburn chamber and then discharged through a chute 7 into a rotary kiln 8.

Rotary kiln 8 slopes downwardly from chute 7 toward a hood 9 that encloses the discharge end of kiln 8 and defines a passage 10 from kiln 8 to a cooler 11. The downward slope of the rotary kiln 8 causes material received from chute 7 to pass through kiln 8, then into hood 9 and through passage 10 to cooler 11.

The cooler 11 is provided with a pair of blowers 12, 13 that blow air upwardly through windboxes 14, 15 and then through material on an air pervious grate 16. A bafile 17 may be provided to define a preliminary cooling chamber 18 and a final cooling chamber 19 over grate 16. As indicated by arrows, cool air supplied by blower 13 is blown upwardly through windbox 15, grate 16 and chamber 19 to be discharged up a stack 20 to the atmosphere. Cool air supplied by blower 12 is blown upwardly through windbox 14, grate 16, chamber 18, and passage 10 into the firing hood 9. A burner 21 is mounted in hood 9 to project into hood 9 to deliver and burn fuel that raises the temperature of gases passing into kiln 8 to the desired high temperature level required for a material receiving a final heat treatment in kiln 8. In plants producing iron ore pellets, cement or lime, the gases entering the kiln will be heated above 2000 degrees Fahrenheit.

Gas flow from the gas discharge end of kiln 8, up chute 7 and into the material preburn chamber 5, will be in a temperature range of about 1600-2100 degrees Fahrenheit, depending upon the nature of the material and the purpose for which it is being heated Gas conveying will now be described that connect preburning chamber 5 to preconditioning chamber 4. A first conduit means is provided that includes windboxes 22 arranged beneath the grate 1 and preburn chamber 5. Each of the windboxes 22 is connected by a conduit systern 23 to one or more cyclone dust collectors 24.

An exhaust opening 25 is defined in housing 2 over grate 1 and opens into preburn chamber 5. A bypass conduit 26 for withdrawing gas from preburn chamber 5 extends from opening 25 and bypasses the stream of material in preburn chamber 5 to discharge into conduit 23 at location 27 upstream from dust collector 24. A damper 28 is placed in conduit 26 to control the flow of bypass gas withdrawn from preburn chamber 5 through opening 25. A damper 29 is arranged to control the flow of cold air through a cold air inlet conduit 30 which discharges cold air into bypass conduit 26 at a location 31.

Dust collector 24 is provided with a solids discharge opening at 32 and a gas discharge opening at 33. A conduit 34 connects the gas discharge opening 33 of dust collector 24, to deliver relatively dust free gas to the inlet 35a of a fan 35. A third damper 36 may be provided along with a second cold air inlet conduit 37 to discharge cold air into conduit 34 at a location 38 downstream of dust collector 24 and upstream of fan 35.

The gas flow system downstream of fan 35 is susceptible of considerable variation depending upon the material being treated and its condition. As shown in the drawing, fan 35 discharges gas from an outlet 35b to a second conduit means shown as a conduit 39 which delivers the gas to preconditioning chamber 4 over grate 1. windbox 40 is arranged beneath grate 1 and chamber 4. A conduit 41 connects windbox 40 to the inlet of a second fan 42. Fan 42 discharges gas received from windbox 40, through a conduit 43 to a stack 44.

The gas flow downstream of fan 35 may be modified to provide an upfiow of gas through material in chamber 4; or windbox 40 and chamber 4 may be subdivided and conduits arranged to provide an upflow through one subchamber and a downfiow of gas through another subchamber; or with a subdivided chamber 4 and windbox- 40, the discharge of fan 35 may be split into two gas streams for delivery to a subdivided chamber 4 and windbox 40 for upfiow or downfiow (or one of each) of gas through such subchambers. If chamber 4 and windbox 40 are subdivided, the subchamber adjacent bafile may be provided with a partial gas bypass to the subchamber remote from bafile 3. Such a bypass system (not shown) may be such 'as has been described with reference numerals 25 through 39.

It is an important feature of the present invention that the arrangement and control of gas fiow from windboxes 22 and bypass exhaust opening 25, to fan 35, provides considerable flexibility for adapting different gas flow pap terns downstream of fan 35 in order to serve the needs of a great variety of materials and process operations.

By way of example only, the operation of the disclosed apparatus will be described as applied to heat hardening pellets of magnetite iron ore (wherein the preburn stage is an exothermic reaction that converts the magnetite to hematite).

Pellets containing magnetite ore are formed in the balling device B and placed upon grate 1 by the feeder F for transport through chamber 4. The heat transfer from gas to pellets in chamber 4 must be carefully con trolled to properly precondition the pellets before they are transported into the preburn chamber 5. That is, in chamber 4 the pellets are dried as they are heated with 750 degrees Fahrenheit gas from about 70 degrees Fahrenheit to an average temperature of about 450 degrees Fahrenheit, but the pellets must not be heated too fastof exposed to too high temperatures in order to avoid pellet breakup and dust formation, and to avoid prematurely initiating the exothermic reaction planned to take place in preburn chamber 5.

The dry pellets at about 450 degrees Fahrenheit preconditioned for preburning are transported into the preburn chamber 5 where they are exposed to temperatures over about 1800 degrees Fahrenheit and the pellets themselves are heated an an average temperature of 1600 degrees Fahrenheit or higher. During this preburn treatment the magnetite Converts to hematite with an exothermic reaction.

After the pellets have been given the desired preburn treatment the body of pellets on grate 1 is disrupted and the pellets are tumbled through kiln 8 and heated to about 2400 degrees Fahrenheit. During this final heat treatment in the kiln some dust is produced and unwanted mineral constituents that may be present, such as arsenic, volatize to gas and vapor. The hot pellets are discharged from kiln 8 and fall through passage 10 to the grate 16 of cooler 11. After the pellets pass through chambers 18 and 19 of cooler 11 they are cooled sufficiently for handling and storage.

The air from chamber 18 of cooler 11, that has been preheated to about 1500 degrees Fahrenheit as it passes through the pellets on grate 16, passes up passage 10 and into kiln 8. The flame and gases from burner 21 mix with the air from cooler 11 to provide an atmosphere in kiln 8 that is over 2400 degrees Fahrenheit. These high temperature gases move counter to the flow of pellets through kiln 8 and with the dust and volatiles from the kiln pass into preburn chamber 5 at over 1800 degrees Fahrenheit.

Damper 28 is adjusted so fan 35 draws about one-third of the gas out exhaust opening 25 into bypass conduit 26 and two-thirds of the gas downwardly through the pellets on grate 1 into windboxes 22 and conduit 23.

The portion of the gas drawn out exhaust opening 25 into bypass conduit 26 unloads most of the dust and unwanted minerals such as arsenic and its compounds. Arsenic and arsenic compounds either condense to form additional dust particles, or as vapor chemically unite with or physically attach to the dust, or a combination of the foregoing possibilities may take place, the exact mechanism is not known or understood. However, two factors are apparent. One factor that is apparent is that most of the arsenic is drawn out of exhaust opening 25 and, after being cooled in a manner that will be described, is discharged from the system through the solids discharge opening 32 in dust collector 24. The second factor that is apparent is that the small amount of arsenic that is not drawn out through exhaust opening 25 remains suspended in the gas flowing through the material on grate 1 in chamber 5. Other unwanted mineral constituents that are volatilized in the kiln are similarly eliminated from the system including alkali from Portland cement and sulfur from lime (when burning limestone to produce lime, the lime may pick up sulfur from the fuel being burned).

Returning to a description of the gas flow system, the gases, vapors and dust drawn out through exhaust opening 25, travel through the bypass conduit 26 to the location marked 31. At the location 31 the cold air inlet conduit 30 admits air at about 70 degrees Fahrenheit into bypass 26. A damper 29 controls the flow of cold air into conduit 25 to drop the temperature of the bypass gas from over 1800 degrees Fahrenheit (upstream of location 31) to about 1100 degrees or less Fahrenheit (downstream of location 31). This bypass gas in conduit 26 and now cooled to 1100 degrees Fahrenheit travels to location 27 where it mixes with gases in conduit 23. The gas in conduit 23 is a blend of gases collected in the windboxes 22 at temperatures in a range from about 550 degrees Fahrenheit (for the windbox nearest bafile 3) to about 1200 degrees Fahrenheit (for the windbox nearest kiln 8). These gases mix in conduit 23 to provide an average gas temperature of about 750 degrees Fahrenheit. Leakage of cool air through various mechanical seals (not shown) between the traveling grate 1 and housing 2 will further cool the gases in conduit 23 to about 700 degrees Fahrenheit. Therefore at location 27, gas in conduit 23 at 700 degrees Fahrenheit and gas in bypass conduit 26 at about 1100 degrees Fahrenheit, mix and provide a gas at about 800 degrees Fahrenheit which then passes into one or more cyclone dust collectors 24.

Dust collectors 24 separate dust particles, such as arsenic compounds, from the gas stream and discharge these materials through opening 32. The material discharged through opening 32 may be leached of material such as arsenic, and the clean iron ore dust may be recirculated through the entire system along with other feed deposited upon the feed end of grate 1, in the manner taught in the Bade patent.

Gas at about 800 degrees Fahrenheit is discharged from dust collector 24 at 33 and may be mixed with additional cool air which may be admitted at location 38, and then delivered by conduit 34 to the inlet of fan 35 at a temperature of about 750 degrees. The gas from fan 35 flows through conduit 39, through chamber 4, the material on grate 1 and into windbox 4-0. This flow heats the material on grate 1 in chamber 4 from degrees Fahrenheit to an average temperature of 450 degrees Fahrenheit and cools the gas from about 750 degree Fahrenheit to about 200 degree Fahrenheit.

In the operation that has been described, the Btu. input by burner 21 and hot gases from the cooler are controlled so that the pellets have been heated in kiln 8 to about 24-00 degrees Fahrenheit and at the material feed end of kiln the gas moving out the kiln is at the rate of approximately one pound of gas at about 1830 degrees Fahrenheit for each pound of solids. Damper 28 is adjus ed so fan 35 pulls out of chamber 5 about .033 pound of gas at 1830 degrees Fahrenheit for each pound of solids in chamber 5 and therefore 0.67 pound of gas at 1830 degrees Fahrenheit, for each pound of solids in chamber 5, is pulled through the bed of material in chamber 5. Damper 29 is adjusted (and damper 36 may also be adjusted when such a damper is provided) so the flow of gas that has been purged of solids and unwanted mineral constituents, and delivered to chamber 4, provides 1.6 pounds of gas at 750 degrees Fahrenheit for each pound of solids in chamber 4. The pounds of solids passing through chambers 4, 5 and kiln 5 is not necessarily the same number of pounds. The reason is that a portion of the solids is withdrawn from the system by the dust collector 24.

With the apparatus and operation that has been described it can now be understood that the present invention provides means for controlling each stage of the furnacing operation to provide the right temperature and quantity of gas for each stage; means for unloading dust from the system for controlling ringing in kiln 8; and means for removing unwanted mineral constituents from the material that are volatilized during the high temperature tumbling of the material in kiln 8.

In an operation processing hematite iron ore burner 6 will likely be used to add heat to the gases in preburn chamber 5.

When processing hematites the percentage of gas that will be withdrawn through exhaust opening 25 may be in the range of only 5 to 10 percent so that in general it can be said that the system can be operated with a by pass of gases in the range of about 5% to 35% or even somewhat higher.

Another desirable and advantageous feature of the apparatus shown in the drawing is the auxiliary stack &5 closed by a cap 46. A lifting assembly 4-7 is connected to cap 46 and operative to lift cap 46 to the position shown in broken lines, to open stack 45. When the plant as shown in the drawing is being prepared for operation and is relatively cool, kiln 8 is heated by fiame from burner 21 to bring kiln 8 up to operating temperatures before material flow is begun. During such warm up periods, and at other times when desired for control purposes, bypass stack 45 is opened to gases from the kiln directly to the atmosphere.

Still other desirable and advantageous features of the apparatus shown in the drawing are the adjustable dampers 48, 49 in the inlets to fans 35, 42, respectively. Dampers 48, 45? provide control of the entire quantity of gas flow through the entire gas conveying means system downstream (in terms of gas fiow) from kiln 3 and preburning chamber 5.

From the foregoing it will be understood that the present invention is possessed of unique advantages. However, such modifications and equivalents of the disclosed concepts such as readily occur to those skilled in the art are intended to be included within the scope of this invention and thus the scope of this invention is intended to be limited only by the scope of the claims such as are, or may hereafter be, appended hereto.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a mineral furnacing apparatus having structures defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series fiow arrangement to define a material flow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a counterfiow of gas from said final heating chamber to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprisin a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber; second conduit means connecting the outlet of said fan to said preconditioning chamber; a bypass conduit connecting a second portion of said preburn chamber to said first conduit means at a location between said preburning chamber and fan; dust collecting and discharging means in said gas conveying means at a location between saidpreburning chamber and said fan; and atmospheric air admitting means connected to said gas conveying means at a location between said preburning chamber and said dust collection and discharging means.

2. In a mineral furnacing apparatus having structures defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series flow arrangement to define a material flow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a coun-.

terfiow of gas from said final heating chamber to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to said preburn chamber at a location on a side of said material stream opposite to the flow of gas through said passage; second conduit means connecting the outlet of said fan to said preconditioning chamber; a bypass conduit connecting said preburn chamber at a location on a side of said material stream facing'the flow of gas through said passage, to said first conduit means at a location between said preburning chamber and said fan, dust collecting and discharging means in said gas conveying means at a location between said preburning chamber and said fan; and atmospheric air admitting means connected to said gas conveying means at a location between said preburning chamber and said dust collection and discharging means.

3. In a mineral furnacing apparatus having structures defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series flow arrangement to define a material fiow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a counterfiow of gas from said final heating chamber to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber; second conduit means connecting the outlet of said fan to said preconditioning chamber; a bypass conduit connecting a second portion of said preburn chamber to said first conduit means at a location between said preburning chamber and said fan; an adjustable damper mounted in said bypass conduit; dust collecting and discharging means in said gas conveying means at a location between said preburning chamber and said fan; and adjustable atmospheric air admitting means connected to said bypass conduit at a location between said adjustable damper and said dust collection and discharging means.

4. In a mineral furnacing apparatus having structure defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series fiow arrangement to define a material fiow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a counterfiow of gas from said final heating chamber to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to said preburn chamber at a location on a side of said material stream opposite to the flow of gas through said passage; second conduit means connecting the outlet of said fan to said preconditioning chamber; a bypass conduit connecting said preburn chamber at a location on a side of said material stream facing the flow of gas through said passage, to said first conduit means at a location between said preburning chamber and said fan, an adjustable damper mounted in said bypass conduit; dust collecting and discharging means in said gas conveying means at a location between said preburning chamber and said fan; and adjustable atmospheric air admitting means connected to said bypass conduit at a location between said adjustable damper and said dust collection and discharging means.

'5. In a mineral furnacing apparatus having structures defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series flow arrangement to define a material flow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a counterfiow of gas from said final heating chamber to said preburning chamber, gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprisin": a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber to said first conduit means at a location between said preburning chamber and said dust collecting and discharging means; and atmospheric air admitting means connected to said gas conveying means at a loca- 9 tion between said preburning chamber and said dust collection and discharging means.

6. In a mineral furnacing apparatus having structures defining at least a chamber for preconditioning material, a chamber for preburning material and a chamber for final heating material, with said chambers being connected together in series flow arrangement to define a material flow stream from said preconditioning chamber to the preburning chamber and then to the final heating chamber, and with means defining a passage for a counterfio w of gas from said final heating chamber to said preburning chamber, gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to said preburn chamber at a location on a side of said material stream opposite to the flow of gas through said passage; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting said preburn chamber at a location on a side of said material stream facing the flow of gas through said passage, to said first conduit means at a location between said preburning chamber and said dust collecting and discharging means; an adjustable damper in said bypass conduit; and adjustable atmospheric air admitting means connected to said bypass conduit at a location between said adjustable damper and said location where said bypass conduit is connected to said first conduit.

7. A mineral furnacing apparatus having a balling device; a feeder; structures defining at least a chamber for preconditioning material, a chamber for preburning ma- .terial, a chamber for final heating material, and a chamber for cooling the heat treated material; said balling device, said feeder and said chambers being connected together in series flow arrangement to define a material flow stream from said balling device to said feeder to said preconditioning chamber to the preburning chamber to the final heating chamber and then to the cooler, and with means defining a passage for a countenfiow of gas from said final heating chamber to said preburning chamber; and gas convey-ing means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means conmeeting the inlet of said fan to said preburn chamber at a location on a side of said material stream opposite to the flow of gas through said passage; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting said preburn chamber at a location on a side of said material stream facing the flow of gas through said passage, to said first conduit means at a location between said preburning chamber and said dust collecting and discharging means; an adjustable damper in said bypass conduit; and adjustable atmospheric air admitting means connected to said bypass conduit at a location between said adjustable damper and said location where said bypass conduit 18 connected to said first conduit.

8. In a mineral furnacing apparatus having a traveling grate enclosed by structures defining at least a chamber for preconditioning material and a chamber for preburning material, rotary kiln for final heating material, said chambers and said kiln being connected together in series fiow arrangement to define a material flow stream from said preconditioning chamber to the preburning chamber and then to said kiln, means defining a passage for a counterflow of gas from said kiln to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit eans connecting the inlet of said fan to a first portion of said preburn chamber below said grate; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber above said grate to said first conduit means at a location between said preburning chamber and said fan; and atmospheric air admitting means connected to said gas conveying means at a location between said preburning chamber and said dust collection and discharging means.

9. In a mineral furnacing apparatus having a traveling grate enclosed by structures defining at least a chamber for preconditioning material and a chamber for preburning material, a rotary kiln for final heating material, said chambers and said kiln being connected together in series flow arrangement to define a material fiow stream from said preconditioning chamber to the preburning chamber and then to said kiln, means defining a passage for a counterfiow of gas from said kiln to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said 'fan to a first portion of said preburn chamber below said grate; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber above said grate to said first conduit means at a first location between said preburning chamber and said dust collecting and discharging means; an adjustable damper mounted in said bypass conduit; and atmospheric air admitting means connected to said bypass conduit at a second location between said damper and first location.

19. A mineral furnacing apparatus having a balling device, a feeder, a traveling grate enclosed by structures defining at least a chamber for preconditioning material and a chamber for preburning material, a rotary kiln for final heating material, a cooler, said chambers, said kiln and said cooler being connected together in a Series fiow arrangement to define a material flow stream from said balling device to said feeder to said preconditioning chamber to the preburning chamber to said kiln and then to said cooler, means defining a passage for a counterliow of gas from said kiln to said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber below said grate; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber above said grate to said first conduit means at a first location between said preburning chamber and said dust collecting and discharging means; an adjustable damper mounted in said bypass conduit; and atmospheric air admitting means connected to said bypass conduit at a second location between said damper and said first location.

11. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning and final heat treating zones and hot dust laden gases from the final heat treating zone are directed into the preburning zone, the steps comprising: drawing a first portion or" said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the preburning zone; bypassing a second portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed second portion of gases to produce a mixture of a temperature lower than gas temperature in said preburning zone; directing the mixture of said bypassed ll 1 second portion of gases and atmospheric air tomove along a cyclonic path; collecting and removing from said mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said mixture to treat the material in said preconditioning zone.

12. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning and final heat treating zones and hot dust laden gases from the final heat treating zone of a temperature in a range from about 16002l00 degrees Fahrenheit are directed into the preburning zone, the steps comprising: drawing a first portion of said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the preburning zone; bypassing a second portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed second portion of gases sufficient to produce a mixture below 1200 degrees Fahrenheit; directing the mixture of said bypassed second portion of gases and atmospheric air to move along a cyclonic path; collecting and removing from said mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said mixture to treat the material in said preconditioning zone.

13. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning and final heat treating zones and hot dust laden gases from the final heat treating zone of a temperature in a range from about l6002l00 degrees Fahrenheit are directed into the preburning zone, the steps comprising: drawing a first portion of said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the pre burning zone; bypassing a second portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed second portion of gases sufiicient to produce a mixture below 850 degrees Fahrenheit; directing the mixture of said bypassed second portion of gases and atmospheric air to move along a cyclonic path; collecting and removing from said mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said mixture to treat the material in said preconditioning zone.

14. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning and final heat treating zones and hot dust laden gases from the final heat treating zone of a temperature in a range from about 1600-2100 degrees Fahrenheit are directed into the preburning zone, the steps comprising: drawing a first portion of said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the preburning zone; bypassing a second portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed second portion of gases sufiicient to produce a first mixture below 1200 degrees Fahrenheit; mixing said first mixture of gases with said first portion of gases to produce a second mixture having a temperature below about '850 degrees Fahrenheit; directing the second mixture of said bypassed second portion of gases, atmospheric air and said first portion of gases to move along a cyclonic path; collecting and removing said second mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said second mixture to treat the material in said preconditioning zone.

15. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning zones and tumbled through a final heat treating zone and hot dust laden gases from the final heat treating zone of a temperature in a range from about 1600-2100 degrees Fahrenheit are directed into the preburning zone, the steps comprising: drawing a first gas portion amounting to 50 to percent of said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the preburning zone; bypassing the remaining portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed portion of gases sufficient to produce a first mixture below 1200 degrees Fahrenheit mixing said first mixture of gases with said first portion of gases to produce a second mixture having a temperature below about 850 degrees Fahrenheit; directing the second mixture of said bypassed second portion of gases, atmopsheric air and said first portion of gases to move along a cyclonic path; collecting and removing from said second mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said second mixture to treat the material in said preconditioning zone.

16. In a method of heat treating mineral material in which material is fed successively through preconditioning, preburning and final heat treating zones and hot dust laden gases from the final heat treating zone are directed into the preburning zone, the steps comprising: admitting a supply of auxiliary heat into said preburning zone; drawing a first portion of said gases in said preburning zone into contact with and through the material in the preburning zone and then out of the preburning zone; bypassing a second portion of said gases in the preburning zone away from material therein and out of the preburning zone; mixing a quantity of air at atmospheric temperature with said bypassed second portion of gases to produce a mixture at a temperature lower than gas temperature in said preburning zone; directing the mixture of said bypassed second portion of gases and atmospheric air to move along a cyclonic path; collecting and removing from said mixture dust particles that are thrown radially outward by said cyclonic movement; and then directing said mixture to treat the material in said preconditioning zone.

17. A mineral furnacing apparatus com-prising a feeder; structures defining at least a chamber for preconditioning material, a chamber for preburning material, a chamber for final heating material, and a chamber for cooling the heat treated material; said feeder and said chambers being connected together in series flow arrangement to define a material flow stream from said feeder to said preconditioning chamber to the preburning chamber to the final heating chamber and then to the cooler, and with means defining a passage for a counterfiow of gas from said cooler to said final heating chamber and said final heating chamber to said preburning chamber; and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to said preburn chamber at a location on a side of said material stream opposite to the flow of gas through said passage; second conduit means connecting the outlet of said fan to said preconditioning chamber; a bypass conduit connecting said preburn chamber at a location on a side of said material stream facing the flow of gas through said passage, to said first conduit means at a location between said preburning chamber and said fan; dust collecting and discharging means in said gas conveying means at a location between said preburning chamber and said fan; and adjustable atmospheric air admitting means connected to said bypass conduit at a location between said preburning chamber and said dust collecting and discharging means.

18. A mineral furnacing apparatus comprising a material agglomerating device, a feeder, a traveling grate enclosed by structures defining at least a chamber for preconditioning material and a chamber for preburning material, rotary kiln for final heating material, and a cooler; said agglomerating device, said feeder, said chambers, said kiln and said cooler being connected together in series flow arrangement to define a material fioW stream therethrou gh; means defining a passage for a counterflow of gas from said cooler to said kiln and said kiln to said preburning chamber; and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber below said grate; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber above said grate to said first conduit means at a location between said preburning chamber and said fan; and atmospheric air admitting means connected to said bypass conduit at a location between said preburning chamber and said dust collection and discharging means.

19. A mineral furnacing apparatus comprising a traveling grate enclosed by structures defining at least a chamber for preconditioning material and a chamber for preburning material, rotary kiln for final heating material, said chambers and said kiln being connected together in series fiow ararngernent to define a material flow stream from said preconditioning chamber to the preburning chamber and then to said kiln, means defining a passage for a counterfiow of gas from said kiln to said preburning chamber, means for admitting an auxiliary supply to heat into said preburning chamber, and gas conveying means connecting said preburning chamber to said preconditioning chamber, said gas conveying means comprising: a fan; first conduit means connecting the inlet of said fan to a first portion of said preburn chamber below said grate; second conduit means connecting the outlet of said fan to said preconditioning chamber; dust collecting and discharging means in said first conduit means for removing dust from said first conduit means; a bypass conduit connecting a second portion of said preburn chamber above said grate to said first conduit means at a location between said preburning chamber and said dust collecting and discharging means; and atmospheric air admitting means connected to said gas conveying means at a location between said preburning chamber and said dust collection and discharging means.

References Cited by the Examiner UNITED STATES PATENTS 2,580,235 12/1951 Lellep 26353 FOREIGN PATENTS 646,452 8/ 1962 Canada. 1,246,265 10/ 1960 France.

FREDERICK L. MATTESON, 111., Primary Examiner.

D. A. TAMBURRO, Assistant Examiner. 

1. IN A MINERAL FURNACING APPARATUS HAVING STRUCTURES DEFINING AT LEAST A CHAMBER FOR PRECONDITIONING MATERIAL, A CHAMBER FOR PREBURNING MATERIAL AND A CHAMBER FOR FINAL HEATING MATERIAL, WITH SAID CHAMBERS BEING CONNECTED TOGETHER IN SERIES FLOW ARRANGEMENT TO DEFINE A MATERIAL FLOW STREAM FROM SAID PRECONDITIONING CHAMBER TO THE PREBURNING CHAMBER AND THEN TO THE FINAL HEATING CHAMBER, AND WITH MEANS DEFINING A PASSAGE FOR A COUNTERFLOW OF GAS FROM SAID FINAL HEATING CHAMBER TO SAID PREBURNING CHAMBER, AND GAS CONVEYING MEANS CONNECTING SAID PREBURNING CHAMBER TO SAID PRECONDITIONING CHAMBER, SAID GAS CONVEYING MEANS COMPRISING: A FAN; FIRST CONDUIT MEANS CONNECTING THE INLET OF SAID FAN TO A FIRST PORTION OF SAID PREBURN CHAMBER; SECOND CONDUIT MEANS CONNECTING THE OUTLET OF SAID FAN TO SAID PRECONDITIONING CHAMBER; A BYPASS CONDUIT CONNECTING A SECOND PORTION OF SAID PREBURN CHAMBER TO SAID FIRST CONDUIT MEANS AT A LOCATION BETWEEN SAID PREBURNING CHAMBER AND FAN; DUST COLLECTING AND DISCHARGING MEANS IN SAID GAS CONVEYING MEANS AT A LOCATION BETWEEN SAID PREBURNING CHAMBER AND SAID FAN; AND ATMOSPHERIC AIR ADMITTING MEANS CONNECTED TO SAID GAS CONVEYING MEANS AT A LOCATION BETWEEN SAID PREBURNING CHAMBER AND SAID DUST COLLECTION AND DISCHARGING MEANS. 